Because huge numbers of southern black-backed gulls have feasted on food in the waste at the Green Island landfill, consent conditions require the Dunedin City Council to manage the food availability there.
The council must also hinder the breeding success of the existing population across the city in order to reduce the existing bird-strike risk to aviation before the landfill is closed and its planned successor at Smooth Hill, 4.5km from Dunedin Airport, opens.
Council waste and environmental solutions group manager Chris Henderson said the number of gulls at Green Island appeared to have started to drop since the introduction of kerbside food and green-waste collections, but gulls had possibly relocated to coastal feeding sites.
‘‘We are yet to see any evidence of a significant decline in the ... population in the wider Dunedin area since population control efforts in 2023.’’
The numbers of gulls at the Green Island landfill varied significantly from month to month.
Two years ago, numbers peaked at about 10,500 in March, before dropping to 1000 in July that year.
The population peaked again at about 13,500 in March last year, before dropping to 1000 in June that year.
Since the introduction of kerbside food and green-waste collection in July last year - now that organic waste was processed separately instead of ending up at the Green Island landfill - the peak number had reduced to about 7100 in February this year.
By March, when numbers usually peaked, the population was 5200.
The way the council was hindering the breeding success involved treating the shells of eggs at nesting sites to reduce the number of successful hatchings. The treatment prevented oxygen transfer, which in turn prevented the embryo from developing, and was a humane population control method, Mr Henderson said.
The council’s southern black-backed gull management plan must include measurable targets and it said the council would halve the number of them in the city by the start of 2028.
By that time there were to be fewer than 100 of the gulls at the landfill and there would be fewer than 5000 at breeding sites plus the landfill.
The council’s targets also include maintaining a very low number of any large birds at Smooth Hill.
